The PCS and WCDMA frequency bands overlap in the USA. This causes problems in dual mode telephones that can operate in either mode.
A dual mode telephone will typical have one antenna for PCS and another for WCDMA. However, because of the overlapping frequency bands, when one antenna is used, the other unused antenna absorbs power from the used antenna which degrades its receiving and transmitting performance. This problem can be solved by isolating the antennas. One way of doing this is to space the antennas far apart, but this is undesirable as it increases the space required for the antennas and the size of the device housing them.